This invention relates to a system for testing the attenuation of an electromagnetic wave transmitting medium, and in particular, to a device for testing the attenuation of fiber optic cables. While the invention is described with particular reference to its use with fiber optic cables in aircraft systems, those skilled in the art will recognize the wider applicability of the inventive principles disclosed hereinafter.
Fiber optic cables are finding increased application in a variety of products, and in particular, in aircraft design. Because of this increased use, instruments for measuring attenuation in such cables are becoming more prevalent. One method of conducting attentuation measuring systems for measuring the attenuation in such fiber optic cables is disclosed in U.S. Pat. No. 4,234,253, issued Nov. 18, 1980, and assigned to the assignee of the present invention. The drawings and specification disclosed in the U.S. Pat. No. 4,234,253 are incorporated herein by reference. In the U.S. Pat. No. 4,234,253, a timing pulse is generated in the receiver and combined with a test signal for transmission. These signals thereafter are separated in the receiver and the timing pulse is used to demodulate the test signal to provide a DC level voltage proportional to the amplitude of the signal wave transmitted through the cable. The DC voltage thus developed was compared with a reference signal and the difference between the received DC voltage and the reference signal was displayed as attenuation.
The invention described hereinafter, while applicable to similar attenuation determining problems, differs from the invention described in the U.S. Pat. No. 4,234,253 in several important design respects. In the present invention, one of the receiver and transmitter is designed to provide what may be considered as a digital signal for processing in the receiver, the digital signal being based on a transmitted reference signal. That is to say, a simple RC network may be utilized to provide a time uniform train of pulses, the pulses decreasing in amplitude by equal decibel values. This train of pulses may be generated at the transmitter and transmitted through a medium under test, or it may be generated in the receiver based on a signal received through the medium from a simplified transmitter. In the first instance, the pulse is used to count down a preset electronic counter. In the second case, the counter counts up. In both cases, the count in the counter after passage of the pulses is displayed as attenuation. When the pulse is generated in the receiver, the receiver, through suitable circuit switching arrangements, may be utilized as an optical power meter. Because of the simplicity of design, the invention provides an extremely low cost, simple and versatile device.
One of the objects of this invention is to provide a system for testing the transmission capabilities of fiber optical conductors.
Another object of this invention is to provide a test system for a medium employing a transmitter and receiver, which may be separate units interconnected only by the medium under test.
Another object of this invention is to provide a test device which functions both as an attenuation meter and a power meter.
Another object of this invention is to provide an attenuation meter for fiber optic cables which utilizes digital processing.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.